It's really quite simple to get going!
Firstly go to the web address above, then tap 'launch a classroom'
You can then share the URL of your whiteboard with the users. I usually email this out to the pupil iPads or associate it with a QR code that can be scanned by pupils.
Once connected all users can draw, add to and edit the whiteboard presentation.
There's an in built chat function and many basic tools, such as pens, text and image insertion.
You can screen capture or email the end results.
Really easy to use and very effective. Great for group work and project planning. Well worth a look!